To remove floatable solids like oil and grease
Explanation
Wastewater treatment plants employ physical processes during the primary treatment stage to separate solids from water. This separation typically occurs in large tanks known as clarifiers or sedimentation tanks, where materials are separated based on their density relative to water.
Detailed Analysis
The components of a sedimentation tank perform distinct functions based on the behavior of the waste materials:
- Skimmer: Substances with a density lower than water, such as oil, grease, and fats, float to the surface. A skimmer is a mechanical arm or device that sweeps across the surface of the tank to collect and remove these floatable solids.
- Scraper: Solids heavier than water, such as faeces and organic matter, settle at the bottom as sludge. A scraper moves along the bottom of the tank to collect this sludge for removal.
- Grit Chamber: Heavy inorganic materials like sand and grit are typically removed in a separate grit chamber prior to the sedimentation tank, not by a skimmer.
- Aerator: Aeration is a biological process (secondary treatment) involving the pumping of air into the water to support bacterial growth; it is not the function of a skimmer.
Key Takeaway: In a sedimentation tank, a skimmer removes low-density floating impurities (oil and grease), whereas a scraper removes high-density settled sludge.